Flange Finish

i think u have to go for the ANSI or BS standards books, these books have much better explanation related to ur issue

From:

http://piping-designer.com/Flange_Facing

ASME B16.5 requires that for flanges and flanged fittings the surface is to have a specific roughness. A concentric or spiral serrated finish with 30 to 55 grooves per inch and a surface roughness between 125 and 500 microinches. This allows different surface grades to be used with various types of gaskets to ensure a tight flange surface. These are some of the common finishes used on raised faces and flat faces.

Types of Finish

• Cold Water - It has a mirror like finish. This is made with a wide tool at a high speed which gives a finished surface much like a ground surface. When a surface has this type of finish it is normally used metal to metal, not with a gasket. It is seldom used in the oil, chemical or related industries.

• Concentric Serrated - A 90° inclined angle tool is used to make the grove. It makes a grove 1/64" deep and 1/32" apart in a concentric circle.

• Smooth - This can be made with several different types of tool shapes. No tool markings will appear to the naked eye on the surface. The roughness of the finish is from 125-250 microinch.

• Spiral Serrated - This is similar to a stock finish but the difference between them is the way the grove is made. A 90° inclined angle tool is used to make the grove. It makes a grove 1/64" deep and the feed is 1/32".

• Stock - The surface is created by a continuous spiral groove. The roughness of the finish is from 125 to 500 microinches and is cut with a tool with an approximately 0.06 inches or larger radius.

I think that SP6 is a finishes spec. If I remember correctly, this specification requires rendering the surface to "clean white metal" - in other words, removal of mill scale. Implicit is sandblasting. This spec typically applies to surface preparation prior to coating - prime paint or other coating. This hardly seems appropriate to the face of a flange.

There are at least two different meanings for "Finish"

The original poster and my answer is directed to the machine "Finish" of a Flange Face.

Your reference to SP6 is directed to the "Finish" as in Painting and Coating.

Two different things, Okay?

@PennPiper and Baffled,

There was a reference in the client document to refer MSS SP 6 for surface finish(machine) for Flat face flange. Since i dnt have access to this standard and from your comments, i reckon that this standard does not say about machine finish but rather to painting and coating.

So i consider to take the finish of flat face flange as per that of standard RF Flange(3.2 to 6.4 micro-meter)only.

Thanks.